v1.0.7: fix: make keep-awake, hotkey, timer and UI actually work

- Register missing KeepAwakeState in Tauri state
- Make Ctrl+Shift+K global shortcut toggle keep-awake via backend
- Rewrite useKeepAwake hook with polling, event sync and error handling
- Highlight active timer preset and add cancel timer button
- Remove fake theme switcher and frontend shortcut registration
- Remove unused tauri plugins (store, shell, os)
- Add missing @tauri-apps/cli dev dependency
- Fix README typo and missing favicon